Technique for measuring overlay between layers of a multilayer structure

Abstract

A method for determining overlay between layers of a multilayer structure may include obtaining a given image representing the multilayer structure, obtaining expected images for layers of the multilayer structure, providing a combined expected image of the multilayer structure as a combination of the expected images of said layers, performing registration of the given image against the combined expected image, and providing segmentation of the given image, thereby producing a segmented image, and maps of the layers of said multilayered structure. The method may further include determining overlay between any two selected layers of the multilayer structure by processing the maps of the two selected layers together with the expected images of said two selected layers.

The invention claimed is: 
     
       1. A method for determining overlay between layers of a multilayer structure, the method comprising:
 receiving a given image representative of the multilayer structure; 
 receiving expected images of layers of the multilayer structure; 
 generating, based on the expected images, a combined expected image of the multilayer structure; 
 registering the given image against the combined expected image; 
 identifying safe areas within the expected images based on probable occlusions and distortions between the expected images and the given image; and 
 computing an overlay measurement between two layers of the multilayer structure based at least partially on the identified safe areas. 
 
     
     
       2. The method according to  claim 1 , further comprising:
 generating segmentation data for the given image; and 
 correcting the segmentation data based at least partially on the computed overlay measurement. 
 
     
     
       3. The method according to  claim 2 , further comprising:
 re-computing the overlay measurement using the corrected segmentation data. 
 
     
     
       4. The method according to  claim 1 , wherein computing the overlay measurement between the two layers of the multilayer structure further comprises:
 performing per-layer registration between a map of a specific layer of the two layers with a respective expected image of the specific layer; 
 for each of the two layers, measuring a shift of the specific layer by comparing the respective map of the specific layer with the respective expected image of the specific layer; and 
 determining the overlay measurement between the two layers based at least partially on a difference between the measured shifts. 
 
     
     
       5. The method according to  claim 4 , further comprising:
 performing the per-layer registration based at least partially on the identified safe areas. 
 
     
     
       6. The method according to  claim 1 , wherein one or more of the expected images of the layers or the combined expected image are design images processed by simulation. 
     
     
       7. The method according to  claim 1 , wherein the multilayer structure is a three-dimensional integrated circuit, and wherein the given image is a scanning electron micrograph of the three-dimensional integrated circuit. 
     
     
       8. A system for image processing comprising:
 a memory to store a given image representative of a multilayer structure and expected images of layers of the multilayer structure; and 
 a processor configured to:
 receive the given image representative of the multilayer structure; 
 receive the expected images of layers of the multilayer structure; 
 generate, based on the expected images, a combined expected image of the multilayer structure; 
 register the given image against the combined expected image; 
 identify safe areas within the expected images based on probable occlusions and distortions between the expected images and the given image; and 
 compute an overlay measurement between two layers of the multilayer structure based at least partially on the identified safe areas. 
 
 
     
     
       9. The system according to  claim 8 , wherein the processor is further configured to:
 generate segmentation data for the given image; and 
 correct the segmentation data based at least partially on the computed overlay measurement. 
 
     
     
       10. The system according to  claim 9 , wherein the processor is further configured to:
 re-compute the overlay measurement using the corrected segmentation data. 
 
     
     
       11. The system according to  claim 8 , wherein to compute the overlay measurement between the two layers of the multilayer structure, the processor is further configured to:
 perform per-layer registration between a map of a specific layer of the two layers with a respective expected image of the specific layer; 
 for each of the two layers, measure a shift of the specific layer by comparing the respective map of the specific layer with the respective expected image of the specific layer; and 
 determine the overlay measurement between the two layers based at least partially on a difference between the measured shifts. 
 
     
     
       12. The system according to  claim 11 , wherein the processor is further configured to:
 perform the per-layer registration based at least partially on the identified safe areas. 
 
     
     
       13. The system according to  claim 8 , wherein one or more of the expected images of the layers or the combined expected image are design images processed by simulation. 
     
     
       14. The system according to  claim 8 , wherein the multilayer structure is a three-dimensional integrated circuit, and wherein the given image is a scanning electron micrograph of the three-dimensional integrated circuit. 
     
     
       15. A non-transitory computer-readable medium having instructions encoded thereon that, when executed by a processor, cause the processor to:
 receive given image representative of a multilayer structure; 
 receive expected images of layers of the multilayer structure; 
 generate, based on the expected images, a combined expected image of the multilayer structure; 
 register the given image against the combined expected image; 
 identify safe areas within the expected images based on probable occlusions and distortions between the expected images and the given image; and 
 compute an overlay measurement between two layers of the multilayer structure based at least partially on the identified safe areas. 
 
     
     
       16. The non-transitory computer-readable medium according to  claim 15 , wherein the processor is to further:
 generate segmentation data for the given image; and 
 correct the segmentation data based at least partially on the computed overlay measurement. 
 
     
     
       17. The non-transitory computer-readable medium according to  claim 16 , wherein the processor is to further:
 re-compute the overlay measurement using the corrected segmentation data. 
 
     
     
       18. The non-transitory computer-readable medium according to  claim 15 , wherein to compute the overlay measurement between the two layers of the multilayer structure, the processor is to further:
 perform per-layer registration between a map of a specific layer of the two layers with a respective expected image of the specific layer; 
 for each of the two layers, measure a shift of the specific layer by comparing the respective map of the specific layer with the respective expected image of the specific layer; and 
 determine the overlay measurement between the two layers based at least partially on a difference between the measured shifts. 
 
     
     
       19. The non-transitory computer-readable medium according to  claim 18 , wherein the processor is to further:
 perform the per-layer registration based at least partially on the identified safe areas. 
 
     
     
       20. The non-transitory computer-readable medium according to  claim 15 , wherein one or more of the expected images of the layers or the combined expected image are design images processed by simulation.